Crystallization Behavior of Poly(l-lactide) Films in Presence of Mg(OH)2 and l-Lactide

The effects of magnesium hydroxide and l-lactide dimer as additives on thermal properties and morphology of poly(l-lactide) (PLLA) films were studied. Hence, neat PLLA films and films containing additives (10% w/w) were prepared in dichloromethane at room temperature via solution casting. To evaluate thermal history on polymer properties, PLLA films were annealed by different processes. In one process, designated as A, PLLAfilms were heated from 20 up 140oC, then held for 1 h and cooled to room temperature. In another process, designated as B, melted PLLA samples which had been maintained at 200oC for 5 min were cooled with a rate of -20oC/min to 140oC and annealed for 1 h before being cooled to room temperature. In the next process designated as C, the melted PLLA samples after 5 min of staying at 200oC were being quenched to 0oC. Then the samples were heated to 140oC followed by annealing for 1 h before being cooled toroom temperature. The crystallization and morphology properties of PLLAfilms were studied using polarized optical microscopy and differential scanningcalorimetry. It is found that the percentage of crystal and spherulitic formationinside PLLA films were influenced by thermal history and presenceof the additives. The type of additives did not affect melting point (Tm) of thefilms annealed through different processes of A to C, while they had influenceon Tm of the films, significantly. It is to be noted that some spheruliteswere formed in films during B process. During C process, however, thenucleation rate increased due to quenching which enhanced the spherulitesformation.